USING S-PARAMETER MEASUREMENTS TO MANAGE SAR AND TRANSMIT GAIN

• US 20100244840A1
• Filed: 03/31/2009
• Published: 09/30/2010
• Est. Priority Date: 03/31/2009
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: McKinnon, Graeme Colin
• Granted Patent: US 8,102,177 B2
• Time in Patent Office: Days
• US Class Current: 324/322
• CPC Class Codes: G01R 33/288 Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room
• CPC Class Codes: G01R 33/3415 comprising arrays of sub-coils , i.e. phased-array coils with flexible receiver channels
• CPC Class Codes: G01R 33/5612 Parallel RF transmission, i.e. RF pulse transmission using a plurality of independent transmission channels
• CPC Class Codes: G01R 33/5659 caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field G01R33/56509, G01R33/56518, G01R33/56536 take precedence

Abstract

Systems and methods for controlling a magnetic resonance imaging system are provided. In one embodiment, a magnetic resonance imaging system includes a radio frequency coil with a plurality of conductive coil elements, control circuitry that determines, based at least in part on a measurement of scattering parameters, a plurality of forward voltages that will cause power deposition into an object within a predetermined specific absorption rate, and an amplifier configured to apply the determined plurality of forward voltages respectively to the plurality of coil elements. The control circuitry may determine the plurality of forward voltages based at least in part on an unloaded measurement of scattering parameters and a loaded measurement of scattering parameters.

Claims

1. A magnetic resonance imaging system comprising:

a radio frequency coil having a plurality of conductive coil elements;

control circuitry configured to determine, based at least in part on a measurement of scattering parameters, a plurality of forward voltages that is predicted to cause a deposition of power into an object within the radio frequency coil when applied respectively to the plurality of coil elements, wherein the deposition of power is within a predetermined specific absorption rate; and

a radio frequency coil amplifier configured to apply the determined plurality of forward voltages respectively to the plurality of coil elements.

2. The system of claim 1, wherein the control circuitry is configured to determine the plurality of forward voltages based at least in part on an unloaded measurement of scattering parameters and a loaded measurement of scattering parameters.

3. The system of claim 1, wherein the control circuitry is configured to determine an impedance of the object based at least in part on an unloaded measurement of scattering parameters and a loaded measurement of scattering parameters.

4. The system of claim 1, wherein the control circuitry is configured to predict an amount of power that will be deposited into the object such that the amount of power is within the predetermined specific absorption rate.

5. The system of claim 1, wherein the control circuitry is configured to determine the plurality of forward voltages based at least in part on a respective plurality of currents through the plurality of coil elements that will cause a predicted amount of power to be deposited.

6. The system of claim 1, comprising a plurality of voltage sensors respectively coupled to cables connecting the plurality of coil elements and the amplifier.

7. The system of claim 6, wherein the plurality of voltage sensors is configured to determine a plurality of reflected voltages that are respectively reflected from the plurality of coil elements.

8. The system of claim 1, wherein the control circuitry is configured to determine the measurement of scattering parameters based at least in part on a plurality of reflected voltages.

9. A magnetic resonance imaging system comprising:

a radio frequency coil assembly configured to obtain a measurement of scattering parameters.

10. The system of claim 9, wherein the radio frequency coil assembly is configured to obtain an unloaded measurement of scattering parameters when an object is not located within the radio frequency coil assembly and to obtain a loaded measurement of scattering parameters when the object is located within the radio frequency coil assembly.

11. The system of claim 9, wherein the radio frequency coil assembly is configured to predict an amount of power that the radio frequency coil assembly will deposit into the object when one or more forward voltages are applied to the radio frequency coil assembly, based at least in part on an unloaded measurement of scattering parameters and a loaded measurement of scattering parameters.

12. The system of claim 9, wherein the radio frequency coil assembly includes a plurality of conductive coil elements.

13. The system of claim 12, wherein the radio frequency coil includes a plurality of sensors connected respectively to the plurality of conductive coil elements, wherein each of the plurality of sensors is configured to determine a reflected voltage when a forward voltage is applied to the respective one of the plurality of conductive coil elements.

14. The system of claim 12, wherein the radio frequency coil assembly is configured to transmit radio frequency pulses to each conductive coil element sequentially and to simultaneously measure reflected voltage at every coil element.

15. The system of claim 9, wherein the radio frequency coil assembly is configured to determine a measurement of scattering parameters based at least in part on measurements of reflected voltage at every coil element.

16. A magnetic resonance imaging system comprising:

a radio frequency coil;

an amplifier configured to drive the radio frequency coil based on a control signal; and

control circuitry operably connected to the amplifier and configured to provide the control signal to the amplifier, the control circuitry capable of;

receiving an unloaded measurement of scattering parameters of the radio frequency coil;

receiving a loaded measurement of scattering parameters of the radio frequency coil; and

determining the control signal, based at least in part on the unloaded measurement of scattering parameters and the loaded measurement of scattering parameters, that is predicted to cause the amplifier to drive the radio frequency coil to deposit an amount of power into an object within the radio frequency coil, wherein the amount of power into the object is within a predetermined specific absorption rate.

17. The system of claim 16, wherein the control circuitry is configured to determine an impedance or an admittance of the object based at least in part on the unloaded measurement of scattering parameters and the loaded measurement of scattering parameters.

18. The system of claim 16, wherein the radio frequency coil comprises a plurality of conductive coil elements.

19. The system of claims 18, wherein the control signal is configured to cause the amplifier to supply a plurality of forward voltage signals respectively to the plurality of conductive coil elements.

20. The system of claim 18, comprising a plurality of voltage sensors connected respectively to the plurality of conductive coil elements, the plurality of voltage sensors being configured to determine a plurality of voltages reflected respectively from the plurality of conductive coil elements when a plurality of forward voltages are respectively applied to the conductive coil elements.